Facing a significant decline in the number of students playing high school football, the New Jersey State Interscholastic Athletic Association on Wednesday adopted new guidelines to sharply reduce the amount of contact allowed in practices and, in doing so, address concerns about player safety.

The new rules, which the association said were the most restrictive in the country, limits the time that teams can engage in full-contact drills in practice to 15 minutes a week, down from the 90 allowed under the old rules. Preseason full-contact drills, previously unlimited, will be reduced to six total hours, including scrimmages.

The existing ban on full contact in spring and summer practices in New Jersey remains in effect. New Jersey officials said that other states are considering similar restrictions as concerns about head injuries continue to grow.

“I think this is a positive thing based on what we know now about player safety and the more education that we are all getting all the time about how to keep players healthy,” said Kevin Carty Jr., the coach at Hillsborough High School in central New Jersey.

The New Jersey association said it implemented the rules on the recommendation of the New Jersey Football Coaches Association and Practice Like Pros, an organization that advocates the exact limits on practices that have now been adopted by New Jersey.

Full contact is considered tackling that brings a player to the ground.

Jesse Mez, an associate professor of neurology at Boston University and member of the school’s Alzheimer’s Center and CTE Center, applauded the new regulations. He said that there is “good evidence” to show a relationship between the dangers of repetitive impacts in football — and not just those involving concussions — and chronic traumatic encephalopathy, the degenerative disease linked to repeated blows to the head. He said the exact nature of that relationship has not been fully measured.

“I think there are better ways of playing team sports and getting exercise than repeatedly hitting your head,” Mez said. “But given the country’s interest in football and how much everybody loves it, if we are not going to stop playing, then we should reduce the amount of contact as much as we can.”

Despite its risks, tackle football is still among the most popular sports for male youths from ages 14 to 17. But participation is falling, and particularly in New Jersey, a state long known for being rich in high school football talent.

In 2017, 1,700 fewer players were reported playing high school football in New Jersey than the year before, a 6.8 percent decrease. Only three states — Colorado, Montana and Oklahoma — lost players at a higher rate over the same period. Most attributed the decline to increased concerns about player safety.

Carty, a past president of the executive board of the New Jersey coaches association, said that while the purpose of the new rules was to increase safety, they also could help slow the decline in participation. He said he and a number of other coaches in New Jersey had been following the guidelines announced Wednesday for the past few seasons. Now, they will apply to everyone.

“We’re not doing this as a recruiting ploy,” he said. “It’s just we want to keep our kids safe and we want people to know this is happening. By making it a mandate statewide, it can ease the fears of a lot of parents that they won’t have to investigate that their coach is doing it the right way.”

Other states moved to put new limits on out-of-game contact before New Jersey did. At least seven allow only 60 minutes of full-contact practice each week, and Texas has also worked to reduce head injuries by offering junior high school and high school coaches seminars on rugby tackling, where the focus is on leading with the shoulder instead of the head.

The N.C.A.A. does not mandate limits for its college football teams, offering only recommendations. The various conferences set their own limits, ranging from the Pacific-12, which allows 90 minutes a week, to the Ivy League, which does not allow any full-contact training.

The N.F.L. allows 14 padded practices during its 18-week regular season, and one practice per day for each day of preseason.

Terry O’Neil, the founder of Practice Like Pros, said that his organization, which includes former N.F.L. players and coaches, neurosurgeons and orthopedists, is not concerned with participation levels. The goal is to promote the safety of those playing the game now. The approval of the New Jersey rules, he said, “is going to be very helpful for us in opening the conversation with other states around the country.”

A version of this article appears in print on , on Page B8 of the New York edition with the headline: Hard-Hitting Practices Curbed at High Schools. Order Reprints | Today’s Paper | Subscribe